The present invention relates to a micro-electro-mechanical actuator, and more particularly to two-dimensional actuator.
Micro-electro-mechanical mirrors have great potential in wide variety of optical applications including laser projection display, optical communication, confocal microscope, laser radar, and etc. For certain optical scanning applications such as scanning laser projection display, the mirror needs to achieve large optical scanning angle at specific frequency under predetermined driving conditions. Large optical scanning angle is also a key to optical resolution and smaller product footprint. For scanning mirror, the requirement poses a challenge in the design of actuator to generate large actuation force.
Conventional electrostatic driven two-dimensional micro-electro-mechanical actuators can be categorized into parallel plate electrodes and comb drive electrodes. In the case of parallel plate electrodes, voltage difference is generated between driving electrode typically positioned beneath the movable mirror which is also served as counter-electrode. Due to the fact that the electrostatic attraction force is inverse proportional to the distance between the mirror and the underneath driving electrode, mirror actuated by parallel plate electrodes does not have large scanning angle in practice. On the other hand, comb drive electrodes are designed to be in interdigitated arrangement to avoid such limitation of parallel pate design, and are preferred for applications requiring large optical scanning angle.
In U.S. Pat. No. 7,271,946B2, Esashi and Kikuchi disclosed a two-dimensional micromirror structure. The comb-drive actuators are designed as vertical comb actuators in staggered three-layer architecture to allow bi-directional rotation of the mirror. The staggered vertical comb-drive actuators may require twice the space of in-plane comb actuator to allow bi-directional rotation of the mirror. Furthermore the vertical comb electrodes in staggered three-layer structure may demand higher precision in manufacturing process comparing to in-plane comb actuator.
In U.S. Pat. No. 6,819,822B2, Behrang Behin, et al described a two-dimensional micro-electro-mechanical scanner with gimbaled architecture driven by vertical interdigitated comb electrodes. The inner part of the gimbal structure can be controlled independently by activating two sets of vertical comb electrodes to allow rotation about two independent axes.
In U.S. Pat. Nos. 7,205,174 and 7,329,930, the inventor of the present invention disclosed the designs and fabrication methods of a micro-electro-mechanical comb-drive actuator with both in-plane and vertical comb electrodes. The multiple-plane comb-drive design enlarges the actuation force and increases the optical scanning angle of the movable element comparing to a vertical comb-drive actuator. The present invention extends the design of micromechanical actuator as described in U.S. Pat. No. 7,329,930 to two dimensional micromechanical actuator using multiple-plane comb electrodes to achieve further functionality.